“Humans are almost entirely the cause” of climate change, according to a scientist who once doubted that global warming even existed.

Last year, Richard Muller walked back years of climate change skepticism in light of new research. But Sunday’s comments go one step further.

Muller wrote in an NYT op-ed that after exhaustive research, he believes that an increase of greenhouse gases can be closely linked to the rise in the earth’s temperature. He explains:

Our results show that the average temperature of the earths land has risen by two and a half degrees Fahrenheit over the past 250 years, including an increase of one and a half degrees over the most recent 50 years. Moreover, it appears likely that essentially all of this increase results from the human emission of greenhouse gases
However, Muller said that he did not believe that the recent heat waves or Hurricane Katrina were caused by global warming.

When they hired him in 1995, the student body president at the University of Nebraska (which Spanier had headed) warned Penn State, saying, "Watch out for his social agenda and make sure he doesn't make it a priority over academics." The warning was prescient.